A recent development in the oil and gas exploration and production industry has been the adoption of expandable bore-lining tubing. This involves running tubing into an open section of bore and then expanding at least a portion of the tubing to a larger diameter. Typically, the upper end of the tubing will overlap the lower end of existing bore-lining casing or liner. In a number of proposals, the upper end of the tubing is expanded initially to create a tubing hanger which serves to fix the tubing in the bore so that the tubing may be disengaged from the running string used to carry the tubing into the bore. Other operations, such as cementing the tubing, or expanding other portions of the tubing, may then take place.
The present applicant has identified that there are certain difficulties involved in creating the initial anchor, particularly in previously cemented tubing. A number of existing proposals suggest the use of radially extendable members for radially extending circumferentially spaced portions of the tubing, to bring the outer surfaces of these portions into engagement with the surrounding casing. However, in any such deformation of metallic tubing, there is a degree of elastic recovery of the tubing once the deforming force has been removed. Thus, the desired degree of engagement between the tubing and the casing may not be achieved.